<!DOCTYPE html>
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<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        function calc(){
            console.log("我是第一个函数");
        }

        function calc2(){
            calc();//在一个函数中去调用另一个函数
        }
        calc2();
        console.log("----");


        function calc3(a,b){
            var sum=a+b;//undefined+undefined  NaN
           
        }
        function calc4(){
            var res=calc3();
            console.log(res);
        }
        calc4();
        console.log("*****");
        function calc3(a,b){
            var sum=a+b;//undefined+undefined  NaN
            return sum;
        }
        function calc4(){
            var res=calc3(100,200);
            console.log(res);
        }
        // calc4();
        calc4();

       
    </script>
</head>
<body>
    
</body>
</html>